Moving from Lie groups to Lie algebras, Adler and Dashen [1]} made a strong case in the 1960s for current algebras in fundamental particle physics. In 1968 Dashen and Sharp [2]} proposed a certain highly singular, local current algebra describing nonrelativistic quantum field theory. Their goal was to describe hadrons by gauge-invariant quantities such as densities and currents, rather than gauge-dependent quantum fields. Behind this work stood earlier ideas of Haag and Kastler [3]} and others on algebras of local observables.
